This disclosure relates to pressure equalization in earphones.
Audio headphones, and in particular, in-ear earphones meant to be seated at least partially in a user's ear canal or ear canal entrance, sometimes have a number of openings, or ports, coupling the volumes within the earphones to the ear canal, to each other, or to free space. As shown in FIG. 1, a typical earphone 10 has a housing 12 defining a front cavity 14 and a rear cavity 16, separated within the body by a electroacoustic transducer, or driver, 18. A main output port 20 couples the front cavity to the ear canal so that the user can hear sound generated by the driver 18. Rear ports 22 and 24 couple the rear cavity to free space to control the acoustic properties of the back cavity and their effect on the audio output or response through the output port 20, as described in U.S. Pat. No. 7,916,888, the entire contents of which are incorporated here by reference. A front port 26 similarly controls the acoustic properties of the front cavity, as described in U.S. Pat. No. 8,594,351, the entire contents of which are incorporated here by reference. The front port 26 also serves as a pressure equalization (PEQ) port because it couples the front cavity to free space. A PEQ port serves to relieve pressure created in the front cavity when the earphone is inserted into the ear. An ear tip 28 serves as an ergonomic interface between the housing 12 and the ear.